1. Field of Invention
The present invention relates to a purine nucleosidase obtained from Ochrobactrum anthropi and to its derivatives, and it further relates to DNA coding for the enzyme or its derivatives, to an expression vector including the DNA, to recombinant host cells transformed with the expression vector, to a process for producing a protein with purine nucleosidase activity using the recombinant host cells, to a process for producing a protein with purine nucleosidase activity using a microorganism belonging to the genus Ochrobactrum capable of producing the protein, and to a process for producing beer or wort using the protein.
2. Related Art
With the westernization and overnutrition of the diet in recent years there has been observed an increase in blood uric acid levels in adult males, leading to fears of a rising number of gout cases due to asymptomatic hyperuricemia. Free purine bases, purine nucleosides, purine nucleotides and high molecular nucleic acids in the diet are digested and absorbed in the digestive tract and decomposed to uric acid by the uric acid cycle in the liver. The vast majority of etiological observations support the view of intake of purine-rich foods as the cause of hyperuricemia and gout, and therefore reduction of ingested purines is the most important means of preventing hyperuricemia and gout.
Purine-rich foods include meat, milt, fish eggs and liver, but alcoholic beverages and especially beer also have rather high purine contents. Actual comparisons of purine contents in various alcoholic beverages by Kaneko (Kiyoko Kaneko, Japan Clin., Vol.49, No.5, 1108-1115, 1991) shows that fermented liquors such as beer, sake and wine contain larger amounts of purines than distilled liquors such as whiskey and Japanese shochu, and that among fermented liquors beer has an especially high purine content. Although the purine content of beer is only 1/100 to 1/10 that of meat, eggs or liver, the comparatively large amount of consumption thereof implies a considerable attack risk for hyperuricemia and gout.
Tofler and Woodings (O. B. Tofler and T. L. Woodings, Med. J. Aust., Vol.2, 479-481, 1981) carried out a follow-up study over 13 years using groups among a survey population classified based on amount of beer consumption, and pointed out a positive correlation between beer consumption and gout frequency. Based on such etiological research conducted to date, beer is considered to be the alcoholic beverage with the highest attack risk for hyperuricemia and gout. However, no technology has been developed for reducing purine levels of foods, including beer.